1. Field
The present disclosed embodiments relate to a loudspeaker system for an aircraft cabin for passengers.
2. Brief Description of Related Developments
In current public address systems in aircraft cabins for reproducing speech announcements, conventional dynamic loudspeakers are used, which are installed in an overhead passenger service unit (PSU) or service duct. Because of the construction and the usually low diaphragm sizes, the loudspeakers develop a very strong directional effect in the medium and high-frequency ranges. This results in a significantly lower sound pressure level away from the preferred direction of the loudspeaker and thus an uneven sound pressure level distribution in the cabin. Outstanding sound and speech quality does result for the seats in the preferred direction of the conventional loudspeaker, but outside the main lobe, only adequate sound and speech quality results at best. In contrast, if the reproduction for the seats away from the preferred direction of the loudspeaker is good, it is perceived as very loud and annoying for the seats in the preferred direction of the loudspeaker, however.
The loudspeakers are safety-relevant and must have their full functional capability and generate the required sound pressure level and speech comprehensibility at a minimal power consumption for a defined time even in case of emergency.
A method and a configuration for achieving more uniform sound distribution properties in cabin loudspeaker operation of air and space vehicles is known from DE 28 19 615 A1. In the configurations, parts of the internal paneling, which is constructed as a honeycomb or sandwich, are provided with an acoustic drive, comprising magnet and oscillating coil, so that they assume the function of a loudspeaker diaphragm. Individual plates of the coffered ceiling and/or the side paneling of the passenger cabin are provided with a sound transducer at appropriate intervals in the cabin. In this prior art, the driver feeds out a force through a movement perpendicular to the main plane of the part, it pushing off against its intrinsic mass of the magnet (mass moment of inertia) or against a rigid retainer.
However, an actually optimal sound level distribution is not yet achieved in the cabin in this prior art either. The degree of freedom for positioning individual sound transducers is increased by using ceiling and side wall paneling elements, but this does not result in the desired effect of uniform sound pressure level distribution because of the partially interrupted sound transmission paths to the hearing location. Thus, for example, with a ceiling installation, the sound illumination is improved in the aisle areas, but this also results in shadowing effects of the baggage compartments located overhead for the seat positions. In the case of integration in side wall elements, a very high volume results through the near field irradiation of seats near the side wall, but a very low volume results due to the strong sound pressure level drop in the transverse direction. In two-aisle cabins, this results in significantly different sound pressures for window seats and middle aisle seats.
In addition, a piezo loudspeaker for improved audio systems in cabins for passengers is known from WO 97/17818. Multiple applications of piezocrystals are disclosed to produce flat loudspeakers of high quality. In particular, multiple flat loudspeaker constructions are specified, which are suitable for aircraft, inter alia.
An acoustic device having an active part is described in US 2002/0027999 A1, in which the distribution of the resonant modes is examined as a function of parameters of the active parts, including the geometric construction and the directionally-dependent rigidity.